Photometric apparatus



May 13, 1941. J. T. NICHOLS PHOTOMETRIC APPARATUS 2 Sheets-Sheet 1 Filed July 2,5, 195e May 13, 1941- J. T. NICHOLS 2,241,557

PHOTOMETRIC APPARATUS Filed July 25, 1936 2 Sheets-Sheet 2 l` 'I4/, da 4 5.5

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JOHN 7.' /V/CHOLS,

Patented May 13, 1941 PHOTOMETBIC APPARATUS John T. Nichols, San Francisco, Calif., assigner,

by mesne assignments, to The Brown Instrument Company, Philadelphia, Pa., a corporation of Pennsylvania.

Application July 25, 1936, kSerial No. 92,646

(ci. ss-zs) uclaims.

This invention relates to photometric apparatus and the like, and is a continuation-in-part of my co-pending application entitled Photometry, bearing Serial #680,887 and filed July 17, 1933; one of my objects being to provide a photometer which operates through the medium of photoelectric cells' in such manner as to provide more accurate results than were hitherto obtainable. Other objects may be inferred from vthe following disclosure of specific examples of my invention.

In the accompanying drawings, Figure 1 schematically illustrates my invention in the form I now consider preferable, and Figure 2 schematically shows another example.

'The preferred form includes a milliameter recorder I and a milliameter indicator 2, which are shown as separate units' although they may be combined into one or either used to the exclusion of the other. Alternating power lines 3 energize the secondary of a transformer 4 which supplies energy to two full wave rectifiers 5 and 5 provided with the usual electric filters for producing a smooth direct current. The rectiiler 9 supplies energy through conductors 1 and 9 to a voltage divider or resistance 9.

'I'his voltage divider provides an electric energizing means for two` similar photoelectric cells III and Il respectively having electron-emissive photocathodes I Ill and II and anodes IIIb and IIb. The anode I9b of the cell I0 and the photocathode IIn of the cell II are connected through conductors I2 and I I to the resistance or energizing means 9, while the anode I Ib of the cell II is connected to the photocathode I0"l of the cell I9 by a conductor I l, the conductor I3 connecting with the negative end of the resistance 9 and the conductor I2 connecting with the resistance 9 at a point positive to the negative end of the latter. `This point is chosen so as to provide the voltage required to properly energize the cells I0 and Il. It is to be here noted that the two cells are connected in series and are energized by the same source of electric current, this being an important feature of the invention to be subsequently explained.

Specifically referring to the voltage divider 9, the line 'I carrying positive current connects with this divider at the point 18, and the line 8 carrying negative current connects with the divider at the point 9*. The line I2 connects with the divider 9 at the point I2a and the line I3 connects at the point 9*, the line 20 connecting at the point 2li'l which is between the points 8a and I 2l. In this manner the results described by the above paragraph are secured.

A conductor I5 connects the conductor I4 to the control grid of an electronic valve I9, the latter including an electron-emissive cathode I9, an anode |61 and the grid I6 to which the conductor I5 connects. The anode lh is connected to the positive end of the resistance 9 by a conductor Il, resistance I8 and conductor I9, while the cathode I9' of the valve I9 is connected by the conductor 20 to the resistance 9 at'a point between the conductors I2 and I3. The cathode I6* ofthe valve I6 is provided with a heater element I9*i powered by a separate transformer 2| having its primary connected to the power lines 9 by lines 9*.

The photocathode I0* of the cell I0 is adapted .to receive light to be measured by way of a focusing lens 22, and an electric lamp 23 is arranged to illuminate the photocathode II' of the cell I I.

A pair of electronic valves 24. which also function as ampliers, are provided. Each has a cathode 24B, an anode 2lb and a control grid 24. A' resistance 25 is electrically energized by the rectier 5 through conductors 29 and 21 which connect with the ends of this resistance. The negative end of this resistance 25 is connected by a conductor 29 to the negative end of the resistance I8, the positive end of the latter being connected to the grids of the valves 24 by way of a conductor 29 which connects with the conductor 1. A conductor 30 connects one end of the iilament of the lamp 23 with the positive end of the resistance 25 through the recorder I and indicator 2, and a conductor 3| connects the other end of this filament with the anodes 2lib of the valves 2l. The cathodes 24S of the valves 24 are heated by being connected to the windings c--c of a transformer 32, the center point 'of these windings being connected by a conductor 33 to a suitable point on the resistance 25.

This transformer 92 is part of the rectifying equipment, the details of the` latter not being more specifically given because they are not considered material at the present time. It also provides windings a-a and b-b which heat the cathodes of the rectiers l and 9.

Operation of the invention in this preferred form is as follows:

Electrons are emitted or liberated from the photocathode Il)a of the photoelectric cell I0 when this photocathode receives light by way of the lens 22. VAs previously explained. this is the current through the lamp 23, and since this lamp-V illuminates the photocathode II of the cell II the emission or liberation of electrons from this photocathode increases. This increase of electrons from the photocathode II tends to make the control grid I5 of the valve I6 less positive.

It is apparent that the current through the lamp 23 will increase until the illumination fromI this source is sufllcient to liberate the same quantlty of electrons from the photocathode II'A of the cell I I as are liberated from the photocathode III'l of the cell I0. Since this condition is de- `pendent on the photocathode IIn being illuminated to the same extent as the photocathode Il, it is possible to measure the light focused by the lens 22 by reading the current through the lamp 23, this being the function of the milliameter recorder I and indicator 2. 'I'hese two instruments may, of course, be calibrated t'o read in any manner desired. 'I'hat isto say, if the light focused by the lens 22 is being measured to determine its illuminating power-the calibrations may be in foot candles, whereas when temperaturel determination is desired the calibrations may bel in degrees Fahrenheit or centigrade.

One of the features of this preferred form is the fact that voltage fluctuations do not materially aect the results obtained. In commercial work voltage fluctuations in the power lines are to be expected, and any apparatus powered by these lines is consequently subjected to these fluctuations. Due to the previously described arrangement of the photoelectric cells and their.

connection to the power lines by way of the voltage divider, both cells are subjected to voltage fluctuations at the same time so that their eilects are nullifled. In other words, since it is the relative conductivities of the two cells which are involved and since the relationship prevails when the fluctuations are the same in the case of each cell, accurate readings result at all times.

It is also to be noted that iluctuations'in the voltage applied to the electronic valves and the lamp illuminating the photoelectric cell balancing the photoelectric cell receiving the light to be measured, cannot materially affect the results obtained. In making this statement it is assumed that the voltage will never reach a point where the capacity of the various elements is exceeded, nor diminish so that it is inadequate to meet the demands of these elements. Obviously, in the case of such extreme fluctuations no apparatus can operate.

Theoretically, the bridge circuit network including the photocells I 0 and II in two adjacent arms, and including the portions of the voltage divider between the points I2n and 20B, and 2lia and 8*, respectively, in its other two arms, can be in stable and exact balance for only one degree of illumination of the cell I0. For that degree of illumination, the equilibrium current flow through ythe lamp 23 may be that resulting from the potential of the grid I6 which is established when the illumination of the cell II is exactly equal to the illumination of the cell Il. For all other degrees of illumination of the cell I0, the relative illuminations of the two cells I0 and I I must diil'er when the potential of the grid I8 is that required to make the current through the lamp 23 that required to bringl the system into equilibrium. With photoelectric cells I0 and II oi' the electron-emissive type described, however, as thosev skilled in the art will recognize, the extent to`which the illumination of the cell I I must differ from that of the cell I3 for di'erent degrees of illumination of the latter, in order that the system may be brought into equilibrium is practically insignificant, and in all equilibrium conditions the said bridge circuit network is thus substantially balanced.

In Figure 2, two photoelectric cells 4I and 42 are connected in vseries by. a line 43 and to batteries 44 `and 45, also connected in series, by

lines 48. It is to be noted that these cells are illustrated as being of the electron-emissive type. The cell 4I is enclosed by a casing 41 and receives its light through a lens 43 and screen 49, it being understood that this light is that which is to bemeasured. The cell 42 is provided with an illuminating lamp 50 whose light must pass through a screen 5I, these elements being shielded against extraneous light by a casing 52. 'I'his lamp is, in eiect, a variable illuminating means.

.A 3-element electronic valve 54 has its4 anode connected to the positive side of the battery 44 through a battery 55 in series therewith. Its `grid is connected to the line 43 between the two cells by a line 55. The valves cathode is connected between the batteries 44 and 45 through a line 51- and resistance 58.

A second 3-element electronic valve 59 is ary ranged with its grid connected to theline 5l. 'I'he lamp 50 is energized through this valve 59, which functions as an electrical valve as well as an amplifier, by batteries 60 and lines 6I and 82, the former connecting to the anode and the latter to the cathode of the valve 59. A battery 63 is in serieswith the batteries 50 and connects through a line 54 to the battery end of the resistance 58. A milliameter indicator or recorder 88 is arranged in series with the lamp 50 to measure the energy used thereby. This instrument may be replaced by a contacting device if the apparatus is to effect some control, or other changes made to suit particular uses.

The operation of the apparatus is as follows:

The cell 4I becomes conductive when it receives light focused on it by the lens 48 and this makes the grid of the valve 54 more positive, causing an increase in the current passing through it and a consequent potential drop in the resistance 58. Therefore, the grid of the valve 59 becomes more positive and consequently causes a greater amount of current to flow through the lamp 5'0. As this lamp brightens, the cell 42 becomes conductive and makes the grid of the valve 54 less positive, and as this valve controls the grid of the valve 59 the latter is also made less positive. Obviously, a balanced condition results, which is dependent on the rel ative conductivities of the two cells, the energy used by the lamp 50 then being an indication of the value of the light being received by the cell 4I. The milliameter 66 indicates or records this measurement and the readings obtained may be converted into units of light measurement.

If the light falling on the cell 4I comes from hot metal, the milliameter readings may be calculated to produce temperature readings directto do so.

ly. In the case of color or shades, the instrument may be calibrated accordingly.

The screens 49 and 5I may be used for various purposes. One of these may be to assure proper black body corrections, as the screens may be colored to transmit monochromatic, red. light only, the Bureau of Standards having already are shown in front of the photoelectric cells.-

In addition to passing only monochromatic light these screens may function to control or regulate the conductivities of the two photoelectric cells, it being understood that these cells as commercially manufactured may not possess the same characteristics.

Furthermore, it is to be understood that the photoelectric cells 4I and 42 are each provided with an electron-emissive photocathode and anode. The electronic valves described obviously may be of the same character described in the preferred form of the invention. In all cases the photoelectric cells are to be distin; guished from selenium cells, photovoltaic cells or any other form of light responsive element not providing electron-emissive photocathodes.

I claim:

, l. The combination of two photoelectric cells each having an electron-emissive photocathode and an anode, an electronic valve having an electron-emissive cathode, an anode and a control grid, means for electrically interconnecting the anode of one of said cells and the photocathode of the other, means for electrically connecting the grid of said valve between said anode and said photocathode of said cells, electric energizing means, an electric resistance, means for electrically connecting said resistance to said f energizing means so as to establish an electric circuit through the former, means for electrically connecting the other anode and the other photocathode of said cells to said resistance vat such points asto negatively energize the photocathodes of said cells, means for electrically connecting the cathode of said valve to said resistance between the connections of said other anode and said other photocathode therewith, illuminating means for the photocathode of one of said cells, the photocathode of the other of said cells being arranged to receive light from another source, an electrically operated control means having no physically moving parts for said illuminating means, electric energizing means for said control means, means in circuit with the anode and cathode of said valve for controlling said control means, and means for measuring the extent said control means is operated. t

2. The combination of two photoelectric cells each having an electron-emissive photocathode and an anode, an electronic valve having an electron-emissive cathode, an anode and a control grid, means for electrically interconnecting ,the anode of one of said cells and the photocathode of the other, means for electrically connecting the grid of said valve between said anode and 4said photocathode of said cells, electric energizing means, means 'for electrically connecting the other anode and the other photocathode of said cells to said energizing means so their photocathodes are negatively energized, means for connecting the cathode oi' said valve to said energizing means so that current from the latter is divided thereby, en electric lamp arranged to illuminate the photocathode oi one of said cells, thephotocathode of the other of said cells bing arranged to receive light from another source, a second electronic valve providing an electron-emissive cathode, an anode and a control grid, electric energizing means for said lamp, means for electrically connecting said lamp to the second named energizing means` lthrough the cathode and anode of the second named valve, a third electric energizing means, means for electrically connecting the cathode and grid of the second named valve to the third named energizing means through the cathode and anode of the rst named valve and means for measuring the current provided said lamp.

3. The combination of two photoelectric cells each having an electron-emissive photocathode and an anode, an electronic valve having an electronic-emissive cathode, an anode and a control grid, means for electrically interconnecting the anode of one of said cells and the photocathode of the other, means for electrically connecting the grid of said valve between said anode and said photocathode of said cells, electric energizing means, an electric resistance, means for electrically connecting said resistance to said energizing means so as to establish an electric circuit through the former, means for electrically connecting the other anode and the other photocathode of said cell to' said resistance at such points as to negatively energize the photocathodes of said cells, means ior electrically connecting the cathode of said valve to said resistance between the connections of said other anode and said other photocathode therewith, an electric lamp arranged to illuminate the photocathode of one of said cells, the photocathode of the other of said cells being arranged to receive light from another source; a second electronic valve providing an electron-emissive cathode, an anode and a control grid, electric energizing means for said lamp, means i'or electrically connecting said lamp to the second named energizing means through the cathode and anode of the second named valve, a third electric energizing means, meansfor electrically connecting the cathode and grid of the second named valve to the third named energizing means through the cathode and anode of the iirst named valve, and means for measuring the current provided said lamp.

4. Photometric apparatus including the combination of two photoelectric cells of the electron-emissive type electrically connected with a source. of electric energy so as to form a normally balanced electric circuit, one of said cells being arranged to receive light from an external source, an electric lamp connected with a source of electric energy and arranged to act as the sole source of illumination for the other of said cells, an electronic valve arranged in circuit with said lamp so as to control the energy supplied to the same, means in said normally balanced circuit which is responsive to any current flow in the same to automatically cause said valve to change the energy supplied said lamp so as to restore Said circuit to its normally balanced condition and means tormeasuring th electric en- I light and the other being provided with an illuminating lamp, a plurality o! current sources arranged in series to energize said cells, a threeelement electronic valve having itsr grid controlled by the current between said cells and current sources, a current source for said lamp, a three-element electronic valve in series with said lamp and having its grid controlled bythe output of the iirst named valve and means for measuring the current passing through said lamp. f

6. Photometric apparatus including the combination oi two photoelectric units of the electron-emissive type electrically connected with a source of electric energy, one of said units being arranged to receive light from an external source, an electric lamp connected with a source of electric energy and arranged to act as the sole source of illumination for the other oi' said cells, an

electronic valve arranged in circuit with said lamp so as to control the energy supplied to the same, means connected in a circuit with said photoelectric umts and said source lof. energy which is responsive to the relative conductivities of the two photoelectric units, which means is active upon change in the relative conductivities of said units caused by a change in the relative amounts of light received by said units to cause said valve to change the energy supplied to said lamp to substantially restore the relation between the amounts of light received by said two cells existing before said change, and means for measuring the electric energy supplied said lamp.

7. Photometric apparatus including the combination of two photoelectric units o1' the electronemisslve type electrically connected with a source of electrical energy, one of said units being arranged to receive light from an external source, a second source of light, arranged to act as the sole source of illumination of the other of said units, solely electrical means including an electrical circuit for controlling the amount 'of illumination supplied by said second source of light to said last mentionedphotoelectric unit, said circuit including energizing means and an electronic valve for controlling the flow oi.' energy through said circuit, means connected in a circuit. with said photoelectric units and said source of electrical energy which is responsive to the relative conductivities of the two photoelectric units, which means is active upon a change in the relative conductivities oi said units, caused by a change in the relative amounts of light received byv said units, to' cause said valve to change the energy supplied to the circuit controlling the amount of illumination supplied by said second source of light to its associated photoelectric unit to substantially restore the relation between the amounts of light received by said two cells existing before said change, and means for measuring the energy supplied to said circuit.

8. In combination, a first light-operated variable resistance device adapted to be subjected to a source of light, an electrical valve including grid means, connections between said rst lightoperated variable resistance device and the grid means of said electrical valve to vary the bias on the gri'd means, a second light-operated variable resistance device, solely electrical means to vary the light to which said second light-operated variable resistance is subjected. connections between said electrical means and electrical valve, connections between the second light-operated variable resistance ,device and the grid means of the electrical valve to vary the bias on said grid means in a direction opposite to which itis varied by said ilrst light-operated variable resistance device, and a device responsive to the resulting ilow of current to said electrical means.

9. In combination, a first photoelectric cell adapted to be subjected to a variable light, a second photoelectric cell, an electric lamp to illuminate said second photoelectric cell, a thermionic device including al plate, a iilament and grid means, a circuit for said lamp controlled by the plate and lament of said thermionic device, connections between said photoelectric cells and grid mans by which said photoelectric cells tend to bias said grid means in oppositel directions to conlointly control the flow .of current to said lamp and a device responsive to the ow I of current to said lamp.

l0. In combination, a first photoelectric cell of the yelectron-emissive type subject to light of unknown value, a second photoelectric cell of the electron-emissive type, means having no mechanically movable parts including an electrical circuit to vary the value of light to which said second photoelectric cell is subjected, current ilow controlling means in control of the current flow in said circuit, connections between the ilrst photoelectric cell and said current ilow controlling means to increase the flow of current through said circuit upon an increase in the value of said unknown light, connections between said second photoelectric cell and said current flow controlling means to decrease the now of current through said circuit uponan increase in the value ofthe light to which the second photoelectric cell is subjected, whereby both of said photoelectric cells control the flow of current through said circuit by operating upon a single current flow controlling means so that variations in the operation of the current ilow controlling means will be at least partially compensated for, and a current responsive device connected to said circuit.

11. Seli balancing apparatus for measuring the magnitude of a variable condition including the combination of an electronic amplifier having an input circuit and an output circuit, a source of energizing voltage, a bridge network receiving energizing current from said source and having its equalizing terminals connected to the input circuit of said amplifier, means included in one arm of said network adapted to change in impedance in accordance with variations in said condition, adjustable means in an opposed arm of said network adapted to be varied for bridge rebalancing purposes, and physically stationary means disposed in the output circuit of said amplifler adapted to control said adjustable means. l2. Self balancing apparatus for measuring the magnitude of a variable condition including the combination of an electronic amplifler having an input; circuit and an output circuit, a source of energizing voltage, a bridge network having a pair of energizing terminals and a pair of equalizing terminals, meansl connecting said energizing terminals to said source of voltage, means connected to said equalizing terminals adapted to opposed arm of said network adapted to be varied for bridge rebalancing purposes, and `physically stationary means disposed in the output circuit lof said amplifier adapted to control said adjustable means.

13. Self balancing apparatus for measuring the magnitude of a variable condition including a network including physically stationary means responsive to the magnitude of said condition and adapted to be unbalanced upon change in 10 said condition from a predetermined value. electronic amplifying means having an input circuit and having an output circuit and responsive to unbalance o! said network, and physically stationary means disposed in the output circuit of 15 said amplifier and adapted to rebalance said network.

14. In combination 4a. photoelectric cell exposed to a variable source oi light, a second photoelectric cell, a bridge circuit including said cells and having equalizing terminals and adapted to be unbalanced by a variation in the relative illumination ot said cells. an electric lamp illuminating said second cell, an electronic amplifier having an input circuit connected to said equalizing terminals. and having an output circuit including a source ot current and said lamp. and means for measuring the current iiow through said lamp.

JOHN T. NICHOLS.V 

